RUSSIAN police searched the homes of prominent opponents of President Vladimir Putin on Monday in a clear warning he is losing patience with dissenters a day before a rally that could draw tens of thousands of people challenging his rule.

RUSSIAN police searched the homes of prominent opponents of President Vladimir Putin on Monday in a clear warning he is losing patience with dissenters a day before a rally that could draw tens of thousands of people challenging his rule.

The searches, which police launched at the apartments of opposition leaders early in the morning, were a new sign Putin is shifting to more aggressive tactics to quash protests as he starts a six-year term.

Putin signed a law on Friday that increased fines for violations of public order at street demonstrations, ignoring warnings from his human rights council that it was unconstitutional. Putin's opponents said the law was an attempt to silence dissent.

Russia's main investigation agency said it planned to conduct about 10 searches in connection with a criminal probe into violence against police at a protest held in Moscow on the eve of Putin's inauguration on May 7.

Opposition leaders Alexei Navalny and Sergei Udaltsov were among those whose Moscow apartments were being searched, the Federal Investigative Committee said on its website. TV presenter Ksenia Sobchak and former Deputy Prime Minister Boris Nemtsov were also among those targeted, activists said.

"There's a search going on at my home," Navalny, an anti-corruption blogger and one of the organisers of protests sparked by allegations of fraud in a December parliamentary election won by Putin's party, said on Twitter.

"They practically cut out the door," wrote Navalny, who later tweeted police had confiscated the electronics in his home "including discs with the children's photos".

Navalny's lawyer was barred from the flat for hours, Ekho Moskvy radio said. His spokeswoman was quoted as saying by Interfax news agency that there were armed police at an office he uses. No one was in the office at the time.

Other members of the opposition said the raids were a sign that Putin had given up on democracy.

"Putin has stopped even imitating democracy," Sergei Mitrokhin, a liberal opposition leader, said on Ekho Moskvy.

Dozens expressed anger over the move on the internet, which the opposition has used to organise the mass protests that have threatened Putin's authority, bypassing a compliant television media that is under tight state control.

"Vova is crazy," one Twitter user wrote, referring to Putin by using the common nickname for Vladimir, and others exchanged messages under the tag that translates as ' h ello1937' – a reference to the deadliest year of Soviet dictator Josef Stalin's repression.

Interfax news agency cited Investigative Committee spokesman Vladimir Markin as saying those whose homes were searched had been summoned to appear at the committee on Tuesday, potentially interfering with their plans for the protest.

Opposition leaders have permission for a march and rally in central Moscow, a test of their ability to maintain pressure on Putin through protests despite the new law increasing fines for protests at which to as much as 300,000 roubles (£6,000) for participants and 1 million roubles for organisers.

Putin won a six-year presidential term in March despite a wave of protests which drew tens of thousands of people to the streets, particularly middle-class city dwellers.

Opposition activists vowed to press ahead with plans for the protest. "These madly repressive measures are meant to frighten people," activist Sergei Davidis said on Ekho Moskvy, adding that the protest would go ahead as planned.